The present invention relates to method and device for measuring biological information in which a specific component having biological information such as glucose, cholesterol, urea, or neutral fat is measured noninvasively by making use of transmitted light, reflected light, scattered light, or transmitted/reflected light.
Recently, a device for measuring glucose of a human subject noninvasively has been proposed.
For example, as described in Yamamura et al., Comprehensive Handbook of Clinical Dermatology 3B: Structure and Function of Skin II, Nakayama Shoten, 1982, it is known that a concentration of glucose in epidermis of a living body changes in direct proportion to a change in a blood-sugar level. Also, as described in Japanese Unexamined Patent Publication No. Hei 5-508336, for example, the method is known in which a near infrared ray of 600 nm-1100 nm is applied to a human subject and a blood-sugar level is obtained by analyzing a light component having a specific wavelength that passed through the human subject.
Further, there has been known the method using a mid infrared ray and an ATR (attenuated total reflectance) prism in which attenuated total reflection of incident light is repeated at an interface between a reflection surface of the ATR prism and a living body, and then light emitted to the outside of the ATR prism is analyzed. For example, in Japanese Laid-Open Patent Publication No. Hei 9-113439, a measuring method by sandwiching an ATR prism in a mouth or between fingers is proposed.
In this method of Japanese Laid-Open Patent Publication No. Hei 9-113439, an evanescent wave (so-called penetrating wave) is applied to a quantitative analysis. A light traveling in an ATR prism slightly seep out into lips or fingers and then is reflected. Therefore, the light is affected by components in a body fluid existing in the lips or fingers. For this reason, variations in reflectance, absorptance, and the like of the body fluid can be detected by measuring the amount of the reflected light, and therefore, information about the components in the body fluid can be obtained.
According to Japanese Unexamined Patent Publication No. Hei 5-508336 and Japanese Laid-Open Patent Publication No. Hei 9-113439 above, since a component such as glucose in a living body has a light absorption peak, when a light of a wave number corresponding to this absorption peak is applied to a living body, the amount of the light absorbed differs corresponding to a glucose concentration in the living body. Therefore, by measuring a returned light from the living body, information regarding a glucose concentration can be obtained. Here, the information regarding a concentration refers to an absolute value of the concentration, variations of the concentration over time, and the like.
Although the evanescent wave is not used, Japanese Laid-Open Patent Publication No. Hei 3-173535 discloses a method in which a glucose concentration in a living body is obtained by applying a near infrared light from a light source to a living body, and energy of a light passed through the living body is measured. To be more specific, a method is proposed in which biological information is measured by passing a light to a finger, specifically to a nail part of the finger.